In U.S. Pat. No. 3,981,481 granted Sept. 21, 1976 assigned to the same assignee as the present application, a bottom operable tank lading loading and unloading valve is disclosed. Such bottom operable tank lading valves allow the operator to operate the lading valve without going on top of the tank. Thus the danger of the operator falling off the tank while operating the lading valve is eliminated.
However during loading and unloading a tank it is necessary to provide a valve to allow air to enter the tank during unloading and allow air to leave the tank while the tank is being loaded. In the past most such air inlet and outlet valves have been located on top of the tank, and operable from the top of the tank. Thus the operator must climb on top of the tank in order to operate such prior art air inlet and outlet valves during loading and unloading the tank.
In application Ser. No. 757,121 filed Jan. 5, 1977, assigned to the same assignee as the present application, an air inlet and outlet valve is mounted within an opening in the top of a transportation tank, for example a railway tank car. The valve is operable from the bottom of the tank by means of an operating shaft which extends from the bottom of the tank up through the tank to the valve. The operating shaft includes shaft telescoping means located within the tank such that the upper part of the operating shaft may move vertically relative to the lower portion of the shaft. As the top of the tank moves relative to the tank bottom, for example under impacts to the tank, the upper portion of the operating shaft will move downwardly relative to the lower portion of the shaft by virtue of the shaft telescoping means, and the valve will remain closed during such downward movement while allowing opening and closing of the valve from the bottom of the car by means of the operating shaft. However the operator must manually open and close this air inlet and outlet valve.
In application Ser. No. 728,343, filed Sept. 30, 1976 a manually operable air inlet and outlet valve is mounted in the bottom of the tank. A conduit extends from the bottom of the tank to a stilling well located in the upper portion of the tank. The stilling well allows air to enter or leave during unloading and loading, and a ball located in the stilling well prevents the lading from entering the conduit and leaving the conduit when the valve is opened. However, again, the operator must manually open and close this air inlet and outlet valve.
It would be desirable to have an air inlet and outlet valve which opens and closes automatically when the bottom operated lading valve is opened and closed, and which will not be damaged when the top of the tank moves downwardly relative to the remainder of the tank.